Muscle Histology Lab
Skeletal muscle 400x (labeled)
See Martini’s, 6th, pp 320-327, Eroschenko’s 9th , pp 75-83.
Muscle is a contractile tissue which generates tension through the molecular pull exerted on actin by myosin fibers in the sarcomere (review these terms in your text). There are three histological classes of muscle, each of which functions in a unique way. Evidence of repeating sarcomere units can be seen in the cross striations of striated and cardiac muscle. The dark “A bands” are arrays of myosin. The light “I bands” are the spaces in between where there is no myosin. Look closely at a longitudinal section of skeletal muscle to see these bands.
I. Smooth muscle cells are tapered at the ends and possess a single centrally located nucleus. Their sarcomeres are not arranged in an orderly repeating fashion, and therefore the cells lack visible striations. These cells are slow contracting, and are responsible for involuntary visceral contractions (peristalsis, uterine contractions, bladder contraction, “bristling” of skin hairs, vasoconstriction, etc).
II. Striated muscle consists of multinucleated fibers produced by the fusion of many individual cells to form a muscle “fiber”. The nuclei and mitochondria are pushed to the outside of the fiber. It owes its striations to regular, repeated arrangement of sarcomeres. It is voluntary, rapid acting, and relatively easily fatigued. It is also known as skeletal muscle, and is responsible for movement of bones.
III. Cardiac muscle, also termed “striated involuntary muscle,” is found only in the heart. Its cells usually contain a single centrally located nucleus, display striations as in striated muscle, but, due to branching interconnections, appear woven together under the microscope. In contrast to striated muscle fibers, their nuclei are centrally located in the fibers. The interconnections between fibers, intercalations, are diagnostic of cardiac muscle but visible only when stained with with iron-containing stains. It is capable of intrinsically initiated rhythmic contraction.
Draw each slide at 400x:
(slide 16) Smooth Muscle.
VE: fig 5-2, p 77
(Draw three or four of these teased out individual smooth muscle cells. These are hard to see, so carefully follow microscope protocol (focus first on the edge of the cover slip).
Features to identify
nuclei located half way between ends of the cells
smooth muscle fibers “spindle” shaped (tapered at each end)
(slide 17) Striated Muscle,
VE: fig 5-3, p 79 and 5-9, p 85
This specimen is from the tongue which is particularly good to show traits of skeletal muscle because it has fibers running at right angles to each other, allowing a longitudinal as well as a cross sections in a single view.
Here is a labeled 450x view of skeletal muscle .
Features to identify
perimysium material binding muscle fascicles together (dark encircling material)
muscle fascicle bundle of muscle fibers: include them in both c. s. and l. s.
endomysium binds individual fibers into a muscle fascicle (lines between fibers)
muscle fiber formed from fused muscle cells, show in both c. s. and l. s.
nuclei of muscle fibers note that they are multiple and pushed to the edge of the fiber
capillaries in endomysium clearly defined round holes at junctions of fibers
A band dark band in the cross striations, corresponds to myosin fibers
I band light band, corresponds to space between ends of myosin
(slide 18) Cardiac Muscle ,
VE: fig 5-7 & 5-10, p 83 & 85
Two slides are shown. The two images are from cardiac muscle stained with hematoxylin-eosin. It shows centrally located nucleii, but not intercalated discs, one of the diagnostic features for cardiac muscle.
Here is a labeled image of cardiac muscle stained with H&E .
The bottom image is cardiac muscle which has been stained with an iron-containing stain which makes the intercalated discs stand out.
Here is a labeled image of cardiac muscle stained with Iron H&E (shows intercalated discs).
Here is another labeled image of cardiac muscle stained with Iron H&E (showing intercalated discs) .
Features to identify
nucleus of cardiac fiber is larger, and is located in central position in cardiac fiber
interwoven fibers characteristic of cardiac muscle
perinuclear sarcoplasm space around the nucleus lacking banding, not seen in striated muscle
intercalated discs join adjacent cardiac fibers end to end, only visible in iron-stained specimens
Muscles of the Head, Trunk and Arms
(Page numbers refer to Pictorial Anatomy of the Cat, rvsd, by Gilbert.)
We will be studying head and trunk muscles of the cat, most of which are analogous to those in the human. Working with a skinned cat ( see previous protocol ) remove cutaneous muscle layer (allows cat to twitch its skin) and a white layer of superficial fascia to better see muscle fiber directions and make the muscles more apparent. Carefully outline, separate and lift the muscles by use of a blunt probe. If the structure in question has multiple fibers in it, it is muscle. Look for intersections between fiber directions, this often indicates two muscles. Fingers are the best blunt probes…
When you need to cut separated superficial muscles to see deep muscles, the superficial muscle to be reflected should be snipped midway between insertion and origin, and laid back to its origin and insertion, noting where they are located. Make four illustrations:
VENTRAL NECK, CHEST AND ABDOMEN:
(See Gilbert, p. 18)
Undissected chest. Remove as much adipose tissue and fascia as you can so that the fibers of the muscles can be seen.
Can you find the pectoantebracialis, pectoralis major, latissimus dorsi and triceps brachii?
Here is the same image with the chest muscles labeled.
Lift deltoid and pectoantebrachialis as a unit and cut and reflect.
Separate pectoralis major from pectoralis minor, cut both, reflect to see: (Gilbert p. 24)
Identify the external muscles of the abdomen (p. 24)
BACK: (p. 22)
Caution: the trapezius is very thin and easily torn when outlining it with the probe. Remove cutaneous muscle layer, note the boundary between trapezoid and the latissimus dorsi which plunges below it.
1. Lift trapezius from underlying latissimus dorsi.
2. Cut and reflect trapezius to see muscles related to or on the scapula: (p. 25). Here is a labeled view of the deep muscles of the back and scapula.
splenius capitis (to the left and below the tip of the probe)
Seen below the rhomboideus muscles.
The “bandage” muscle in the posterior neck.
Origin: upper thoracic spinous processes.
Insertion: mastoid process. process
Here again is a labeled view of the deep muscles of the back and scapula.
Muscles of the shoulders and arms
Brachial plexus: To be studied Winter Quarter:
deltoid and cutting the latissimus dorsi so that it can be reflected:
Cutting the pectoralis. The trapezius has been cut and reflected to show the scapula and rhomboideuses